We propose to conduct a pilot study to determine the feasibility of a factorial trial of selenium and vitamins A and E as chemoprophylactic agents against cancer. In animal experiments these agents have effectively decreased the incidence of tumors induced by a variety of carcinogens. In addition, the trial will include vitamin B6, which may reduce the occurrence of coronary heart disease (CHD). This pilot study will be conducted among a sample of 2,000 male American dentists 40 years of age and older, who would also form the population for the full-scale trial. A questionnaire will be sent to potential participants inquiring about past medical events, recognized risk factors for cancer and CHD, and current dietary intake. In addition, we will provide a brief description of the proposed trial and ask dentists if they would consider participating in it. If they respond positively, we will send them a detailed description of the study and a consent form. Consenting dentists will be randomized to one of the 16 combinations of retinyl acetate, (25,000 IU daily), vitamin E (400 IU daily), vitamin B6 (10 mgm daily), selenium (200 micrograms daily) and placebo. These preparations will be combined so that each participant will take only one pill daily. The outcomes of direct interest in this study will be the participation rate of dentists and compliance with treatment assignment, assessed after 6 and 12 months of treatment by both questionnaire data and blood analyses among a sub-sample of participants. These data will determine whether a full-scale trial with sufficient power can be conducted.